1. Field of the Invention
This invention relates to a die bonder which fabricates semiconductor devices.
2. Description of the Related Art
A semiconductor device is formed by mounting semiconductor pellets onto a base such as lead frame or substrate for BGA (Ball Grid Array) using a die bonder. Then the plurality of pellet mounting parts are arranged and performing resin molding at a subsequent step.
Conventional lead frames are made of metal plate and formed by punching, and even if a part of a lead frame is not good (no-good), a pellet is mounted on such part. In another words, a die bonder is formed on the assumption that pellets are mounted on all islands (die pads) of the lead frame.
The current need for reduction in size accelerates the transition to such as BGAs or CSPs (Chip Size Package). However, because of the complicated structures a substrate of such package might have some no-good part. It means that, even if a few no-good parts are included in the substrate, other good parts must be used from an economical viewpoint. Therefore, functions are provided to give a bad mark to the no-good part in the substrate so that the no-good part can be identified by a die bonder, to bond a pellet only to a good part without mounting a pellet on a no-good part. Normally, a wafer is divided and supplied, while the arrangement of pellets is substantially maintained, and good pellets without marks are picked up. When the pellets are bonded onto island of the substrate, the substrate is checked, and if a bad mark is found on the substrate, the marked part is passed without bonding a pellet-and the next island is fed.
However, such bonding may cause a situation in which substrates with pellet mounted and some of substrates without pellet mounted are supplied together to a subsequent step. When such substrates are processed under the same condition at the subsequent resin molding steps into each of which resins are injected, it will cause different capacities, variations in the quality of products. Moreover, the resin might leak from a part, where no pellet is provided, and the resin attaches to a mold holding a substrate and is cured. Since the cured resin cannot be easily removed, a measure is taken to avoid the problem by bonding a dummy pellet to a no-good island. For these reasons, there is a necessity of providing a die bonder which can bond no-good pellets to no-good islands and which can bond a dummy pellet to a no-good island.
It is an object of this invention to provide a die bonder which picks up and bonds a good pellet to a good pellet mounting part (called xe2x80x9cislandxe2x80x9d) of a substrate and bonds a no-good pellet to a no-good island.
To achieve the aforementioned object, this invention provides a die bonder, to which semiconductor pellets are supplied in a systematically arranged state, comprising a substrate feeding mechanism including a plurality of islands to position the island, a no-good detecting means to detect no-good island, and a pellet transfer mechanism, which picks up and carries a good pellet to a bonding position when an island in bonding position is good, and mounts a no-good pellet when an island is no-good. As described above, when the no-good detecting means judges that an island is no-good, then a no-good pellet is mounted.
In the die bonder of the present invention, semiconductor pellets including no-good pellets are supplied in an arranged state. The die bonder comprises a substrate feeding mechanism for feeding a substrate including a plurality of islands to position the islands at a bonding position, a no-good detecting means for detecting no-good island and a pellet transfer mechanism. The pellet transfer mechanism may be formed to pick up and carry a good pellet to a bonding position in the order of the arrangement of semiconductor pellets, leaving no-good pellets unpicked when a island at the bonding position is good. And when a island is judged as no-good one, the mechanism picks up, carries, and mounts one of no-good pellets. Conventionally, pellets are arranged on a wafer and carried to the die bonder so that no-good pellets are also carried to the bonder. In this bonder, it is not required to separately prepare no-good pellets.
Further, the die bonder, to which semiconductor pellets are supplied including no-good ones in an arranged state, may comprise a substrate feeding mechanism including a plurality of islands to successively set the islands at bonding position, a no-good detecting means for detecting no-good island, a stocker for stocking a plurality of no-good pellets, and a pellet carrying mechanism. When an island set at a bonding position is no-good, then the bonder picks up and carries a good pellet to the bonding position for mounting in the order of the pellet layout. When a no-good pellet is detected, the bonder picks up and carries the no-good pellet into the stocker if the stocker is not occupied, or leaves the pellet unpicked if the stocker is occupied. And if an island is no-good, the bonder picks up and carries a no-good pellet from the stocker to the bonding position for mounting. This allows the supplied pellets to be picked up in the order of the arrangement, and hence the bonder is not complicated, simplifying the software of the bonder. No-good pellets can be immediately picked up since they are stocked in the stocker.
The die bonder of the invention is to bond semiconductor pellets to a substrate or base material such as a lead frame or a substrate for CSP having a plurality of pellet mounting parts (called xe2x80x9cislandxe2x80x9d). The substrate may include a no-good island. The die bonder includes a substrate feeding mechanism for carrying the substrate in such a manner that the islands are successively set at a predetermined bonding position, in a manner similar to a conventional die bonder.
Since the substrate may have no-good islands, a detecting means for detecting no-good island is provided to prevent expensive good pellets from being mounted onto a land. As the no-good detecting means, an image processing device including a camera which is disposed at the bonding position or before the bonding position and which takes an image near the island or another sensor may be used to check defects by the on-the-spot observation, or similar means or simpler means may be used to check a mark (bad mark) assigned to a no-good island at a test beforehand.
The pellets are supplied in an arranged state to the die bonder of the present invention. In many aspects, the arrangement of the pellets is maintained on a wafer and hence the pellets are supplied, including no-good pellets. However, a die bonder can basically select only good pellets and put on a chip tray in an arranged state. This kind of die bonder may be employed to supply defective pellets, being put on a similar chip tray, to bond them to no-good islands, while good pellets are picked up from the chip tray and bonded to good island.
On the other hand, in the die bonder of the type in which pellets are supplied, together with no-good pellets, there are two methods to bond the pellets to good islands, as follows. In a first method, good pellets are picked up and carried to a bonding position in the order of the pellets arrangement, leaving a no-good pellet unpicked. And if no-good island is set at the bonding position, the carrying order is changed to pick up the no-good pellet to mount it onto the no-good island. So if a good island is set at the bonding position, a good pellet is picked up and bonded. This method can be employed without the necessity of changing devices. However, when the substrate has many no-good island and a wafer having few no-good pellets is supplied, the bonder may have to be stopped since no-good pellets are all picked up from preceding wafers and can not be used.
In a second method, a stocker for stocking no-good pellets is provided. If a good island is set at a bonding position, a good pellet is picked up and bonded in the order of the arrangement of pellets. If a no-good pellet is detected, it is picked up and carried into a space of the stocker, if available, and if not available, it is left without being picked up. If a no-good island is set at the bonding position, a no-good pellet in the stocker is picked up and bonded. The stocker is provided for stocking no-good pellets to prevent the lack thereof. The stocker may be made for free movement to pick up or receive no-good pellets at a required position, or the stocker may be fixed and a pellet transfer mechanism is made for free movement in XY directions. According to this method, since the semiconductor pellets can be picked up in order, a pickup operation can be performed at a higher speed.
In any of the aforementioned methods, a pellet transfer mechanism is provided. The pellet transfer mechanism picks up and carries a supplied pellet to bond it to a island of a substrate positioned at a bonding position, and picks up, carries, and puts a no-good pellet into a stocker, and picks up and carries a no-good pellet stored in the stocker or in a chip tray to a island positioned at the bonding position. As the pellet transfer mechanism, a pick-and-place mechanism which utilizes vacuum suction is often used. The aforementioned carrying operations may be performed by a single pick-and-place mechanism, or each or some of the operations may be performed by a separate pick-and-place mechanism. In addition, a series of operations of picking up, carrying, and bonding pellets supplied to the islands may be carried out by a first pick-and-place mechanism which picks up and temporarily places pellets at a relay point, where after accurate positioning is made, and a second pick-and-place mechanism picks up, carries, and bonds the pellets to a island. The pellet transfer mechanism described in the specification is composed of all of such mechanisms.
For picking up the supplied semiconductor pellets, a method may be used, in which a wafer stage (carrier stage if the pellets are supplied in a chip carrier) on which pellets are arranged, is provided to be movable in XY directions to set pellets to be picked up at a predetermined pickup position and a pellet transfer mechanism performs a pickup operation at a fixed point. Alternatively, a method may be used, in which the semiconductor pellets are fixed and the pellet carrying mechanism moves in XY directions to pick up the pellets.
For separating good pellets from no-good pellets when the pellets comprising good and no-good ones are supplied, a method can be applied. For example, each of the no-good pellets is assigned a mark (bad mark) in a wafer stage, and the bonder is provided with a detecting means including an image processing device such as a camera for photographing a pellet to check a mark and the external appearance of pellet. Alternatively, there is another method in which pellets are supplied where a wafer is divided into individual pellets substantially maintaining the original arrangement and a map data showing no-good and good pellets in a wafer stage is provided for the die bonder. Then defective pellets can be identified by using the map data only.
When a no-good pellet stocker is not provided and pellets including no-good pellets are supplied and if a good island is set at a bonding position, the good pellet is picked up, and carried to the bonding position, leaving the no-good pellet. And, if a no-good island is set at the bonding position, a no-good pellet must be picked up and bonded. In the method for detecting no-good pellets based on a map data, a no-good pellet can be taken up using the map data. On the other hand, in the method for detecting no-good pellet by providing the no-good pellet detecting means to check a mark on the spot, search is performed to find no-good pellet, in which the positions of the pellets previously left unpicked are preferably memorized.